ci-artifacts: build git-for-windows/git, not git/git, for the UCRT64 SDK

Cloning git/git's `master` does not allow compiling for UCRT64; This
change has to be upstreamed from Git for Windows yet.

So let's build git-for-windows/git, for now.

Assisted-by: Opus 4.7
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.github/workflows/ci-artifacts.yml

@@ -44,9 +44,12 @@ jobs:
         with:
           name: minimal-sdk
           path: git-sdk-x86_64-minimal.tar.gz
-      - name: clone git.git's `master`
-        run: git clone --depth=1 --branch master https://github.com/git/git ..\git
-      - name: build current `master` of git.git
+      - name: clone git-for-windows/git's `main`
+        shell: bash
+        run: |
+          git clone --depth=1 --branch main \
+            https://github.com/git-for-windows/git ../git
+      - name: build current `main` of git-for-windows/git
         shell: bash
         run: |
           set -x